Web Site, Site Collection
SharePoint enables you, as the administrator, to create a new web site with its own URL. Let the technical people deal with getting the URL set. You need to know that your site will be hosted on a specific web address. Technical people call this a Fully Qualified Domain Name (FQDN). Something like https://yourcompany.sharePoint/site.
Document libraries are collections of files that can be shared with other users. Document Libraries are key to SharePoint Document Management (DM) features. Think of the places you will need to share documents. Maybe HR, or a specific project, or a team. Document Libraries give you a place to share documents in a structured way.
Finally the most popular SharePoint feature is the Team Site. A team site is a basic web page which contains lists and document libraries. Generally you create a team site in SharePoint any time you have a requirement to make a "small web page" for a specific purpose. Don't use Team Sites for resent you companies entire strategy. Think of them as small web pages with set purposes.
Once the IT guys have given you a Team Site define the Document Libraries, lists, columns and content types you will need to meet the business objectives. SharePoint builds on simply tools to give you the power to quickly implement the Information Architecture you want, without having to write code or go through long testing processes.